ELECTROCHEMISTRY - Wits Structural Chemistry

4/1/2010
Reaction at cathode =
Reaction at anode =
Zn(s) Zn 2+ (aq) + 2e - Cu2+(aq) + 2e- Cu(s)
Oxidation:
Reduction:
Salt bridge:
‣ Completes the circuit.
‣ Maintains electrical neutrality in the two
compartments by migration of ions
through the porous material.
‣ No further redox reaction will take place if
electrical neutrality is not maintained.
‣Prevents mixing of the electrode solutions.
Molecular view:
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The 2e - ’s move through the circuit to the Cu strip.
Cell Notation:
Oxidation at anode
Reduction at cathode
Separate
phases
electrode in soln
Salt
bridge
Separate
phases
in soln electrode
Zn(s) Zn 2+ (1 M) Cu 2+ (1 M) Cu(s)
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On the Zn strip, a Zn atom
“looses” 2e - ’s to form Zn 2+
which moves into solution.
When the Cu 2+ ions collide with
the Cu strip, 2e - ’s are
transferred to form Cu o
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Cell EMF
E cell depends on:
Why do electrons flow in the direction they do
Due to the potential difference between the 2
electrodes (or difference in potential energy)
Electrons at the anode have a higher potential
energy than the electrons at the cathode
electrons spontaneously flow from
anode to cathode
The potential difference is the driving force that
pushes electrons through the circuit
= electromotive force = EMF
= cell voltage
= cell potential = E cell
• the reactions that occur at the electrodes
• the concentrations of reactants and products
• temperature (assume 25 o C unless otherwise stated)
E cell > 0 for a SPONTANEOUS cell reaction!
By convention
E o cell = standard cell potential
Standard conditions:
1 M concentration for reactants & products
1 atm pressure for gases
Zn(s) + Cu 2+ (aq,1M) Zn 2+ (aq,1M) + Cu(s)
E o cell = +1.10 V
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